Check if you get big memory spikes when transferring, or OOM entries in dmesg.
Had some trouble with a new samba install on Debian causing OOM issues recently (this was admittedly in LXC). Resulted in files apparently transfered but were not. This was due to optimistic locks, which are apparently poorly implemented (according to the 2-year old open bug) but on by default. I haven't done due diligence to say what's the best solution, I just turned oplocks off.
Check if you get big memory spikes when transferring, or OOM entries in dmesg.
Had some trouble with a new samba install on Debian causing OOM issues recently (this was admittedly in LXC). Resulted in files apparently transfered but were not. This was due to optimistic locks, which are apparently poorly implemented (according to the 2-year old open bug) but on by default. I haven't done due diligence to say what's the best solution, I just turned oplocks off.
https://bugzilla.samba.org/show_bug.cgi?id=15261